South Carolina, Nevada, North Dakota and ME also will choose candidates for the November 6 races that could help determine control of the U.S. Senate and House of Representatives, including two of the most competitive Senate races.

"Scott Walker and his Republican allies gerrymandered this district for their own partisan benefit, but the the citizens of Wisconsin are clearly speaking out this year to demand a state government that better represents their values", Holder said in a statement.

In Nevada, Democrats face a contentious primary that could cost them the victory in November.

As recently as the 1990s, Democrats and Republicans were fairly even divided in Nevada, a state that had supported Republican presidents including Ronald Reagan, George H.W. Bush and his son, George W. Bush. Tim Kaine for his seat in the U.S. Senate.

Republican strategists acknowledge voter enthusiasm appears high among Democrats, but they attribute that more to there being a stronger field of blue candidates than in past years.

Local elections officials are reporting low turnout so far across Virginia in Tuesday's primary.

Democrats hope to extend momentum seen in Democrat Patty Schachtner winning an open seat in a conservative northwestern Wisconsin state Senate district in January. "Nevadans deserve a senator we can trust to always put Nevada first, and I'm going to keep earning the support of voters across this state as we work to flip this seat".

Democrat Susie Lee cruised to an easy primary victory in a key congressional race in Nevada, setting up a battle in November for the seat left open when U.S. Rep. Jacky Rosen chose to run for Senate. Rep. Mark Sanford, R-S.C., a vocal Trump critic, is facing a serious challenge from Republican state Rep. Katie Arrington, a Trump supporter who has attacked the state's former governor for being too critical of the president.

We asked the Director of Elections and Voter Registration for Greenville County why voters should care about this year's primaries. Republican Mary Mayhew is the only woman running in a four-candidate Republican primary.